Present hot air sport balloons include a generally sphere-like envelope having an open mouth at the lower end, and certain models include an apex opening at the upper end. The apex opening is selectively covered and uncovered by a circular valve panel, which is controllable by the pilot to permit a controlled venting or deflation of the envelope. A carriage is mounted below the mouth of the envelope for supporting the pilot and other passengers, and a gas burner is mounted on the carriage for heating the air within the envelope.
Hot air ballooning has become an increasingly popular sport in recent years. In virtually all balloons, the hot air required for buoyancy is generated by a burner which uses propane as a fuel. Typical flight durations with these balloons are from one to two hours. However, by carrying a very heavy overload of fuel, a few flights over twelve hours have been possible for hot air balloons. These long flights are for special record-breaking attempts and are not practical for the sport balloonist.
While relatively short flights of one or two hours may be acceptable to many balloonists, it would be most desirable to make longer flights as is commonly the case with gas balloons such as those containing hydrogen or helium. With gas balloons, typical flight durations are more in the range of five to fifteen hours. To make hot air balloons fly, it is necessary to heat air within the balloon sufficiently so that the mass of internal air is less than the mass of the surrounding air by an amount equal to the mass of the balloon and its load.
Additional fuel is required in order to achieve the longer flight time. However, additional fuel not only results in greater hazard because of the presence of flammable fuel but in greater weight.
Additionally, hot air balloons suffer from the problem that during pressurization of the envelope with combustion device it is necessary to hold the envelope stationary to prevent contact of the envelope with hot surfaces that may melt the thin fabric structure. This is not always possible since ballooning primarily occurs outdoors where the balloon is subjected to winds. To avoid the problems of contact with hot surfaces there have been utilized skirts or scoops about the mount or throat of the balloons which acts as a flame barrier. Also, inlet nozzles have been utilized to direct the heated gases into the mouth of the balloon. The flame barriers, skirts and scoops have been generally constructed with fabrics comprising flame retarding high performance fibers such as Kelvar, Nomex or Kynol. Unfortunately, these prior art fabrics add a large amount of additional weight and still are not effective in preventing scorching of the materials if the flame accidently contacts the fabric.
The envelopes of present balloons typically are composed of a plurality of four sided fabric panels, which are interconnected to form a number of vertical gores which extend from the mouth to the apex or deflation port. Light weight fabric such as ripstop nylon and polyester are generally used. To make the envelope non-pervious, the interior is usually coated with polyurethane. Such fabric structures have a maximum operating temperature of 250.degree. F. Temperatures between 250.degree. and 275.degree. F. can only be utilized for only 10 minutes. The lower temperatures are necessary to obtain greater longevity of the fabric since it deteriorates at high temperatures and because of pollutants in the heated gases.